Registration of the kind mentioned above is already known, e.g. from the Swedish patent No. 7413396-8. This publication describes a so-called audio or noise dosimeter, which includes a microphone transmitting an electrical signal in response to sound picked up by it, said signal being supplied to two parallel light-emitting diode (L.E.D.) circuits after filtering and amplification. Each circuit has a LED, which is energised for emitting light when the input signal to the circuit is within a given interval corresponding to a given sound level interval. Each LED has allotted to it a given portion of a photographic film, where the emission flow of the associated LED is detected and integratingly recorded as a film darkening. After a recording process, which may include an arbitrary time period, either continuous or comprising partial periods, the film will accordingly carry a number of integrated measurement value registrations (dose records) corresponding to the number of measurement intervals, i.e. to the number of LEDs, each registration representing the noise dose for the associated measurement interval. The respective noise doses may be subsequently established by determining the degree of darkening (after developing the film) on the respective portions of the film by comparison with known degrees of darkening, e.g. in a so-called densiometer.
A recording apparatus that is constructed in accordance with the known principles described above affords a number of advantages, such as: Permitting registration of measured quantity sequences having very short duration, e.g. sound impulses; Operation entirely without moving parts; Easily miniaturizable utilizing modern transducer and other circuit and electronics components, making it particularly well suited to applications for personal wear.
This known kind of registering apparatus has a clear disadvantage however, since the actual determination of an obtained measurement value is complicated, and requires densiometric equipment or other similar, advanced laboratory equipment.